1. Field of the Invention
The present invention relates to an IC tag communication system provided with a plurality of reader antennas.
2. Description of the Related Art
Although a passive-type IC tag is convenient as it has no power source of its own, it requires a supply of sufficient power for its operation. Therefore, a communication distance between a reader (reader unit) of an RFID tag system using the passive-type IC tag and the passive-type IC tag depends upon whether an IC chip in the IC tag receives sufficient power for its activation and whether an answering wave from the IC chip can be received by a reader antenna. In order to increase a communication distance, the following two methods can be considered: (1) Increase an output from the reader antenna; and (2) Reduce power required to activate the IC chip. However, the method of (1) is limited in terms of regulation, influence on other devices, influence on the human body, and the like and it is technically difficult to overcome the limitations. Although the method of (2) has been improved in various aspects, there is a limitation in the power reduction.
For these reasons, there is a certain degree of limitation on the communication distance of the passive-type IC tag. Thus, in the case where the communication distance exceeds a certain threshold, the RFID system needs to use an active-type IC tag having power source of its own. However, since the active-type IC tag has a power source as described above, the tag becomes expensive, leading to increased cost of the entire system.
Further, in order to increase the communication distance of the passive-type IC tag, a system having a plurality of reader antennas has been proposed. In this case, a supply of power to the IC tag is controlled by switching the reader antennas. For example, Jpn. Pat. Appln. Laid-Open Publication No. 2001-116583 discloses a destination guidance system that detects the current area of the RFID based on which antenna a signal from the RFID (IC tag) has been received by.
However, irrespective of using the passive-type or active-type IC tag, a use of a plurality of reader antennas creates interference issue between the IC tag and the antennas, preventing a satisfactory communication between the IC tag and reader unit.
The present invention has been made in view of the above problem involved in the conventional IC tag communication system and an object thereof is to provide an IC tag communication system capable of satisfactorily communicating with an IC tag in a configuration having a plurality of reader antennas.
According to an aspect of the present invention, there is provided an IC tag communication system including: a plurality of reader antennas which receive radio waves emitted from an IC tag attached to an article, the radio waves being at least partly overlapped with each other; a plurality of readers which are connected respectively to the reader antennas; and a phase adjustment section for adjusting the phases of the radio waves that the reader antennas receive to each other.
According to the aspect, an IC tag communication system capable of satisfactorily communicating with an IC tag in a configuration having a plurality of reader antennas can be obtained.